Three examples of non-enzymatic homogenous, metal-catalyzed photolysis of water are known at present in the literature.J.-M. Lehn and J.-P. Sauvage (Nouv. J. Chim. 1, 1977, 449) describe a four-component system consisting of tris (.alpha.,.alpha.'-dipyridyl) ruthenium (II) dichloride, the mild reducing agent triethanolamine, a "rhodiumbipyridyl complex" and K.sub.2 PtCl.sub.6. Upon exposure to light in aqueous solution, this system produces a maximum of 4 ml H.sub.2 in 1.5 hours.
H. Kagan et al. (Nouv. J. Chim. 2, 1978, 547) used a slightly modified system: tris (.alpha.,.alpha.'-dipyridyl) ruthenium (II) dichloride, ethylene diamine tetraacetic acid, methylviologen, and colloidal platinum or gold. They obtained a maximum of 10 ml of H.sub.2 in roughly 10 hours.
J. Kiwi and M. Gratzel published a system almost identical to that of Kagan (Helv. Chim. Acta 61, 2720) in which the platinum or gold in Kagan's catalyst system was merely replaced by PtO.sub.2 (Adams' catalyst). These authors obtained 0.4 ml of H.sub.2 in 0.5 hours.
If photochemical generation of hydrogen from water is to have any practical significance, there is clearly a need to increase the rates of hydrogen production by photochemical disintegration of water.